Electric utilities using coal-fired power plants are often faced with the problem of disposing of increasingly large volumes of coal combustion by-products (CCBP). These CCBP include fly ash, bottom ash and flue-gas desulfurization sludge, which is a mixture of calcium sulfite/calcium sulphate.
Fly ash is a finely divided non-combustible residue which results from the burning of coal or lignite. Fly ash comprises silicon oxide, alumina, ferric oxides and calcium oxide. Fly ash is known to be a natural pozzolan, and sets up rapidly when combined with water. Bottom ash is a non-combustible granular material which falls to the bottom a furnace during coal or lignite combustion. Bottom ash is coarser than fly ash and ranges in size from a size approximating that of fine sand to coarse gravel. Hydrated fly ash and bottom ash mixtures have concrete-like properties which include high compressive strength and excellent weathering characteristics.
Given the large volumes of CCBP produced and the increasingly limited scope for disposing of this by-product in conventional land fills, there is an increasing need for utilities to find imaginative alternative to CCBP disposal. Consequently, the electric utilities have sought ways and means to use CCBP in, for example, the construction industry as an additive to concrete to produce light weight concrete.
At the same time that the utilities are faced with the problem of disposing of large quantities of CCBP, coastal development projects require a large amount of material for reef enhancement projects For example, the U.S. Corps of Engineers is currently, in 1991, involved in diverting the Colorado River near its mouth at Matagorda, Tex., back to its original course. This will allow the river to empty into Matagorda Bay. This project will require replacement of sufficient substrate to create 54 oyster reefs in Matagorda Bay. These reefs will use approximately one hundred thousand cubic yards of material. As a further example, the proposed deepening and widening of the Houston Ship Channel in Galveston Bay, Tex., if approved, would probably require the establishment of several hundred acres of oyster reef. It is also significant that increased fishing pressure off-shore has caused a decline in populations of important sport and commercial fish species. The Texas Parks and Wildlife Department has formed an Artificial Reef Advisory Committee in an effort to create new off-shore habitats for these declining fish populations.
Currently, oyster and clam shells are the most commonly used substrate for the creation and enhancement of reefs. These materials have historically been obtained by dredging buried shell deposits. However, this source of supply is rapidly declining and therefore becoming more costly. Furthermore, the dredging of shell deposits is currently strictly forbidden in Texas waters. Coastal states are now seeking alternative reef substrate materials.